Amorphous polyolefins are well known and are very useful in adhesives, roofing compositions, cable filing, cable flooding, and caulks and sealants. Amorphous polyolefins are produced and then transferred or shipped in many different forms for incorporation into final compositions. Amorphous polyolefins are generally tacky at room temperature and have a low degree of crystallinity and therefore are not easily formed into powders or pellets for shipment. Amorphous polyolefins are generally transferred in the molten state in large containers or small and large blocks packaged in a release coated paper container and in some instances as small slats coated with a non-tacky substance packaged in corrugated containers.
A preferred form to transfer amorphous polyolefins is in the bulk molten form. The bulk molten form is preferred due to its low processing cost. However, the bulk molten form is shipped in large containers such as tank cars and many end users do not have the capability to unload or store these large quantities of molten amorphous polyolefins. However, the use of the solid block form of amorphous polyolefin is very labor intensive, requiring the end user to remove the coated paper prior to blending. The paper is often adhered to the APO and difficult to remove and also generates solid waste. The larger solid form i.e. 50 pound package is generally preferred over the 20 pound package due to the reduced time spent to remove the package from around the block per any given amount of amorphous polyolefin. Due to the difficulties associated with the molten or block forms, many end users would prefer amorphous polyolefin packaged in an economical and easy to use solid form.
Compounders or end users of the amorphous polyolefin prefer forms of the solid amorphous polyolefin that are easy to handle. Amorphous polyolefin pellets would be most desirable, however, their production is very difficult and they are not commercially available. Thus, of the available forms, amorphous polyolefin slats are generally the form most preferred and easiest to handle. However, it was discovered that some amorphous polyolefins cannot even be formed into slats.
It has been found that certain polymeric compounds that are inherently “soft and tacky” such as certain amorphous polypropylene copolymers are extremely difficult to process into the form of usable slats. These materials must then be produced and sold in some other less desirable form.
EASTOFLEX E1003 from Eastman Chemical Company is one such amorphous propylene ethylene copolymer in that it is a low viscosity (less than 1000 cP at 190° C.) amorphous propylene copolymer with a relatively high comonomer (ethylene) content. These characteristics make the material very soft and pressure sensitive. The material is so soft, that it cannot be considered a “solid” at room temperature (23° C.). This, in combination with its tack, make the polymer extremely difficult to handle as anything but a molten liquid. For this reason, an alternate method for handling materials like E1003 is needed.
As stated above a normal means to handle an amorphous polyolefin or hot melt adhesive is to pour the molten material into a silicone coated release container in the form of a block. It is easy enough to fill materials like E1003 into this type of carton, but not so easy to remove them from the container. E1003 will not release from silicone coated release paper at typical ambient conditions. The polymer has very low cohesive strength and would rather stick to the release paper than to itself. It's low cohesive strength is represented by its low tensile strength (less than 150 kPa). Another indication of an APOs tensile strength is its needle penetration value. The higher the needle penetration value, the softer and weaker the polymer and E1003 has a needle penetration value greater than 95 dmm at 23° C.
Another problem with trying to use materials like E1003 with this type of package is that one needs to physically grab the material while trying to separate the release coated container from the E1003. Since E1003 is not a solid at typical ambient conditions, one cannot grab the material to pull it away from the carton. It sticks to hands, gets between fingers and still does not separate from the release coated container. One way to get around this problem is to cool the product to <0° C. to harden (strengthen) the polymer before removing it from the container. This works fine except that a large freezer is required to store significant quantities of materials like E1003 and the final product is used molten, thus cooling the product right before melting it is a waste of time and energy.
The current method of packaging materials like E1003 is to put it into a release lined fiber drum. The drum is designed to be used with a “drum unloader”, where a heated platen is inserted into the drum and pumps the material off as it melts. However, most end users do not have this type of equipment because of their high cost. So, most end users try to cut through the drum, pry it open and dig out the E1003. This is extremely difficult, very labor intensive and messy.
Another common method of processing amorphous polyolefins and hot melt adhesives is to extrude the materials, quench cool them then cut or chop them into their final physical form (slats). However, some amorphous polyolefins, such as E1003 are difficult to extrude, cut or chop, because they are too soft and tacky after melt extruding and quench cooling that they do not feed well into the cutting device (deform under the pressure of the take up device) or they deform under shear forces in the cutter or chopper and gum up or wrap the cutting blade(s). The majority of amorphous polyolefins slat (term for coextrusion of amorphous polyolefins with non-tacky polyolefin material) very well. In general, butene and hexene copolymers slat at lower rates than propylene homopolymers and ethylene copolymers with needle penetrations less than 40 dmm at 23° C.
In light of the above, it would be very desirable to be able to produce a solid form of low viscosity, low tensile strength, tacky amorphous propylene copolymers that is convenient to use and does not require the labor to unwrap.